Telephone-circuit



(No Model.)

H. S. THORNBERRY.

- TELEPHONE CIRCUIT. I No. 317,888. Patented May 12, 1885.

X Is l W dth/eases. fnvenzzo NITE rains n'inivr mien.

TELEPHONE-CERCUIT.

SPECIFICATION forming part of Letters Patent No; 317,888, dated May 12, 1885.

Application filed November 8, 1884. (No model.)

ToaZZ whom it may concern.-

Be it known that I, HENRY S. THORNBERRY, of Boston, in the county of Suffolk and State of Massachusetts, have invented certain Improvements in Telephone-Circuits, of which the following is a specification.

The object of my invention is to obviate the evil effects of inductive and other similar disturbances on telephone-lines.

It is well known that when two electrical conductors are placed in proximity sudden variations of the electrical condition in one will produce variations in the other more or less pronounced, according to the nature of such variations and the proximity of the two conductors in question. The effect of this action of one current upon another is very apparent in telephonic instruments, and to obviate the ill effects thereof resort is had to the use of a complete metallic circuit, wherein the telephone-instruments are placed. I have discovered that in using such circuits between points widely separated the two terminal stations can converse much more freely and uninterruptedly if no intermediate stations are in circuit; or, to state the fact in other words, it has been found that the introduction of instruments at stations intermediate between the terminal stations operates to render apparent such interfering and troublesome electrical effects as the use of the metallic circuit is calculated to avoid. This seems to be due to the disturbance of the electrical balance existing between the two sides of the metallic loop, caused by the introduction of a resistance and the production of an electrical effect (as the magneto-electric inductive) in one side of the metallic circuit or loop only, and my invention is designed to remedy this difficulty.

To this end my invention consists in the method of obviating inductive or disturbing effects in a metallic circuit; and it consists in producing and maintaining an electrical balance between the two sides of such circuit by introducing into one side of said loop or circuit means to compensate or balance the effect produced by the introduction of the telephone and accompanying instruments in the other side. For this purpose I place at intermediate stations an adjustable electrical resistance, as a coil of wire, more or less of which may be included in the circuit, having a core adjustable with respect to its exposure to said coil, as by inserting said core to a greater or less extent within the coil. Means are provided at the station whereby the telephone-set may be inserted in one side of the loop and the compensating device in the other, the disturbing effects referred to being thus eliminated. WVhen the telephone is not in use, it is customary to insert an electro-mag-neticindieating instrument, as an annunciator, and when the telephone-set is replaced in circuit by such indicatinginstrument the device provided to balance the effect produced by its presence must be correspondingly varied.

The accompanying drawing illustrates my invention.

A and B are two stations at the opposite terminals of a metallic circuit.

0 is an intermediate station. Each station is equipped with telephone-sets and indicating-instruments of any known or desired form. At 0 there is, for instance, a hand-telephone,

H, and induction-coil I, in the primary of 7:

Which is a transmitter, T, preferably of the contact-varying species. There is also an indicating instrument or annunciator, as a. At station 0 is also placed an adjustable resistance, which may be in the form of a coil, X. A series of connections, w, are so arranged and connected from different points in the coil to a commutator having connections, as Pand 19, that more or less resistance may be included in the main circuit. The corecis also adjustable with respect to its exposure to the coils of resistance X, as indicated by dotted lines, whereby the inductive action occurring by reason of its presence may be regulated to neutralize that of the telephone-set or indicatinginstrument in the other side of the loop.

WVhen the telephone-set is removed from circuit and an annunciator, as a, is inserted, the compensating device must be adjusted to cor respond with such change, and vice versa. An electrical balance is thus provided and maintained and the disturbing effects above referred to obviated.

Having described my invention, what I claim, and desire to secure by Letters Patent, 1s-

1. The combination, at a station arranged for telephonic communication, of a telephone or indicating instrument located in one side of a metallic circuit or loop, and an adjustable resistance substantially equal thereto located 5 in the other side of said circuit or loop.

2. The combination, at a station arranged for telephonic communication, of a telephone located in one side of a metallic circuit or loop, and an adjustable resistance-coil having a core 10 adjustable with respect to the extent of its insertion therein located in the other side of said circuit or loop.

3. The combination, at a station arranged for telephonic communication, of a telephone 15 or indicating instrument located in the first side of a metallic circuit or loop, and means, such as a resistance, located in the second side of said circuit or loop, for producing an electrical effect substantially equal to the effect due to the presence of the said telephone or 20 indicating instrument in the first side.

In testimony whereof "I have signed my name to this specification, in the presence of two subscribing witnesses, this 6th day of N ovember, 1884.

H. S. THORNBERRY.

Witnesses:

WM. B. VANSIZE, G120. WILLIs PIERCE. 

